Measurement of Packing Fraction in Polarized Ammonia Targets

Accurate determination of the packing fraction is essential in polarized target experiments, as it quantifies the fraction of active scattering nuclei within the target material. Commonly used polarized targets, such as glassy matrices or crystallized ammonia, are chosen for their favorable polarization properties under beam conditions. However, since these materials do not fully occupy the target cell volume, precise measurement of the packing fraction is necessary to properly normalize experimental yields and extract meaningful cross sections and asymmetries. We present a technique recently developed at the University of Virginia for high-precision packing fraction measurement, along with alternative estimation methods for cases where information is limited. Together, these approaches offer a practical and reproducible framework for target characterization in spin-dependent scattering experiments.